Apparatus for creating a chorus or celeste effect with an electronic musical instrument



onpzmm'm APPARATUS FOR CREATING A CHORUS OR CELESTE EFFECT Filed April 19, 1968 J SZABO WITH AN ELECTRONIC MUSICAL INSTRUMENT 4 Sheets-Sheet 1 b TRIGGER I I l V jl l l VOLTS VOIJ'S TIME w FIG. 3b I I.

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VOLTS Flcasa 7 TIME vouw FIG 5b 0 nus-+- FlG5c 0 TIME INVENTOR JOHN SZABO PATENT AGEN 0d. 20, 1970 sz Bo 3,535,431

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JOHN SZABO PATENT AGENT,-

United States Patent Oifice 3,535,431 Patented Oct. 20, 1970 U.S. Cl. 841.11 14 Claims ABSTRACT OF THE DISCLOSURE A tone signal generator is connected to a frequency modifying device having two output terminals at which appear two signals each having a frequency differing from the frequency of the tone signal. At least one of these signals is amplitude modulated and then is added to the other signal.

The invention relates to apparatus for use in an electronic musical instrument, more specifically, an electronic organ, for creating a chorus or celeste effect.

The tone of an electronic organ often is criticized for lacking the warmth or pleasing qualities that are inherent in the tone of a pipe organ. The advantage that a pipe organ has over an electronic organ in this respect is due mainly to the large number of individual tone producing pipes whose pitch and phase relation to ane another are not fixed, so that when any two or more pipes of essentially the same pitch or octavely related pitch are sounded together, the resultant complex tone appears to change at regular periods due to cancellation and addition of some components of the tones produced by each sounding pipe depending on the phase relation of the tones at any time during the aforementioned regular periods. The resulting effect is called chorus or celeste effect depending on the frequency of the regular periods.

There are several methods in which chorus or celeste effects are or have been simulated in electronic organs, e.g., the use of two or more sets of tone generators, dctuning of the octavely related oscillators, or frequency modulation of individual oscillators at different rates. Such methods either are too expensive or are not appliable to the most popular and inexpensive tone generator systems which use bistable flip-flop frequency dividers to derive octavely related tone signals. The inherent disadvantage of such a tone generator system is that all octavely related tones are precisely in tune and have a fixed phase relation with respect to each other, and, therefore, the chorus effect is lacking.

In accordance with this invention, there is provided a simple and inexpensive tone generator system of the frequency divider or multiplier type capable of producing a chorus or celeste effect. The chorus or celeste effect can be switched on or off as desired and can be controlled easily by the player with respect to both intensity and rate.

In brief, in accordance with this invention there is provided a tone signal generator having an output terminal and adapted to provide a tone signal at its output terminal. A frequency divider or multiplier having an input terminal and first and second output terminals has its output terminal connected to the output terminal of the tone signal generator, whereby the tone signal is supplied to the frequency modifier and the latter provides first and second signals at its first and second output terminals respectively, these signals both having a frequency different from the frequency of the tone signal. An amplitude modulator modulates at least one of the first and second signals, one of which is shaped to have a waveform different than the other, and means are provided for adding the amplitude modulated one of the signals and the other one of the first and second signals.

This invention will become more apparent from the following detailed description, taken in conjunction with the appended drawings, in which:

FIG. 1 is a circuit diagram of a frequency divider which is in the form of a bistable multivibrator or flip-flop, and two shaping networks;

FIGS. 2a and 2b show the voltage waveforms produced at two of the output terminals of the network of FIG. 1;

FIG. 20 shows the sum of the voltage waveforms illustrated in FIGS. 2a and 2b;

FIGS. 3a, 3b and 3c correspond to FIGS. 2a, 2b and 20 respectively except for the voltage waveform of FIG, 3a having half. the amplitude of the voltage waveform of FIG. 2a;

FIGS. 4a, 4b and 4c correspond to FIGS. 2a, 2b and 20 respectively except for the voltage waveform of FIG. 4a being at a different output terminal than the output terminal at which the voltage Waveform of FIG. 2a appears;

FIGS. 5a, 5b and 5c correspond to FIGS. 4a, 4b and 40 respectively except for the voltage waveform of FIG. 5b having half the amplitude of the voltage waveform of FIG. 4b

FIG. 6 is a block diagram of a tone generator system embodying this invention;

FIG. 7 is a block diagram of another tone generator system embodying this invention;

FIG. 8 shows the voltage waveform produced at the output terminal of the modulating signal source shown in FIG. 9;

FIG. 9 is a block and circuit diagram of a part of the tone generator system shown in FIG. 6;

FIG. 10 is a wiring diagram of a system having four modulating signal sources and forty-eight control terminals;

FIGS. 11a, 11b, 11c and 11d show the voltage waveforms at the output terminals of the four modulating signal sources of FIG. 10; and

FIG. 12 is a wiring diagram of a system similar to the system of FIG. 10 but having sixteen modulating signal sources.

Referring to FIG. 1, the network within the dotted line v10 thereof is a conventional bistable multivibrator or flip-flop. It consists of resistors R1, R2, R3, R4 and R5, capacitors C1 and C2 and transistors TR1 and TR2. The base electrode of transistor TR1 is connected via the parallel connected combination of resistor R5 and capacitor C2 to the collector electrode of transistor TR2, while the base electrode of transistor TR2 is connected via the parallel connected combination of resistor R4 and capacitor C1 to the collector electrode of transistor TR1. The emitter electrodes of the two transistors are connected to a DC reference potential, which is shown as ground potential in the figure. The collector electrode of transistor TR1 is connected via series connected resistors R2 and R1 to a source of positive DC potential (B+). Similarly, the collector electrode of transistor TR2 is connected via series connected resistors R3 and R1 to the source of positive DC potential.

A trigger signal input terminal 11 is connected via a coupling capacitor C3 to the terminal of the flip-flop common to resistors R1, R2 and R3.

Two waveform shaping networks are provided, one consisting of a resistor R6, a capacitor C4 and a diode D1, and the other consisting of a resistor R7, a capacitor C5 and a diode D2. Resistor R7 and capacitor C5 are connected in series circuit between the terminal 12. at B+ potential and the terminal 13 at ground potential. The common terminal of resistor R7 and capacitor C5 is connected to the anode of diode D2, while the cathode of diode D2 is connected to the collector electrode of transistor TR1. Similarly, resistor R6 and capacitor C4 are connected in series circuit between terminals 12 and 13, the common terminal of resistor R6 and capacitor C4 being connected to the anode of diode D1, and the cathode of diode D1 being connected to the collector electrode of transistor TR2.

The complete network of FIG. 1 has three output terminals 14, 15 and 16-, terminal 14 being connected via a resistor R8 to the collector electrode of transistor TRl, terminal 15 being connected to the common terminal of resistor R7, capacitor C and diode D2, and terminal 16 being connected to the common terminal of resistor R6, capacitor C4 and diode D1.

The operation of the flip-flop shown in FIG. 1 is well known in the art. When B+ is applied to terminal 12, one of transistors TRl and TR2 will conduct holding the other transistor off. Upon application of a suitable trigger signal to input terminal 11, the flip-flop will change state, the transistor that was previously turned on being turned olf, and the transistor that was previously turned oif being turned on. The flip-flop will revert to its original state upon applictaion of another trigger signal to input terminal 11.

If regularly recurring trigger pulses are applied to input terminal 11, a waveform of the type shown in 2a will appear at the output terminal 18 of the flip-flop, this waveform being a square waveform. An identical waveform will appear at the output terminal 17 of the flipflop, except that the waveform appearing at output terminal 17 will be 180 degrees out of phase with the waveform appearing at output terminal 18. Consequently, if these two waveforms were added, complete cancellation would result.

In accordance wth one aspect of this invention, one of the two waveforms appearing at terminals 17 and 18 is so altered that when the altered waveform is added with the unaltered waveform, complete cancellation does not result. There are many ways to so alter one of the waveforms to achieve this result. Thus, if the signal at output terminal 17 of the flip-flop is applied to the shaping network consisting of diode D1, resistor R6 and capacitor C4, the waveform appearing at output terminal 16 will be as shown in FIG. 2b. If the signal that appears at output terminal 18, which signal is shown in FIG. 2a, is added to the signal that appears at output terminal 16, which signal is shown in FIG. 2b, the result will be the waveform shown in FIG. 20. Complete cancellation has not resulted, but there is a change of both harmonic content and phase. If, by proper selection of resistor R8, the signal appearing at output terminal 14 has one-half the amplitude of the signal at output terminal 18, it would appear as shown in FIG. 3a. If the signals appearing at output terminals 14 and 16 were added, the signal appearing at output terminal 16 being as shown in FIG. 3b, the result would be the waveform shown in FIG. 30. It will be apparent that if the amplitude of the signal appearing at output terminals 14 or 18 were varied from zero to the maximum shown in 2a, the sum of this signal and the signal appearing at output terminal 16 would vary be tween the waveform of FIG. 2b and the waveform of FIG. 20, the waveform of FIG. 30 being obtained when the signal at output terminal 14 or 18 has the amplitude shown in FIG. 3a. At no time do the two output signals cancel each other, but rather a change in waveform and hence in tone character results.

Referring now to FIGS. 4a, 4b, and 40, with regularly recurring trigger pulses applied to input terminal 11, the signal appearing at output terminal 15 will be as shown in FIG. 4a, while the signal appearing at output terminal 16 will be as shown in FIG. 4b. Addition of these two signals, which are 180 out of phase, but otherwise identical, will result in the waveform of FIG. 40.

If the amplitude of the signal appearing at output terminal 16 were one-half that of the signal appearing at output terminal 15', the waveform of the; signal at output terminal 16 would be as shown in FIG. 5b, whereas the waveform of the signal appearing at output terminal 15 would be as shown in FIG. Sa. If these two signals were added, the waveform of FIG. 50 would result. If the amplitude of the signal appearing at output terminal 16 were varied from zero to the maximum amplitude shown in FIG. 4b, the sum of the signals appearing at output terminals 15 and 16 would vary in waveform from that shown in FIG. 4a to that shown in FIG. 4c, the waveform of FIG. 50 being obtained when the waveform at output terminal 16 was as shown in FIG. 5b.

It should be noted that with waveforms of the type shown in FIGS. 4a and 4b, addition thereof causes cancollation of the fundamental frequency, and only the harmonics remain from the second harmonic up. The cancellation of the fundamental frequency is similar to that condition which results when two signals of similar frequency and amplitudeare added.

It should be apparent from the foregoing that by shaping one or both output signals of the flip-flop, modulating the amplitude of the shaped or unshaped signal and then adding the resulting signals, a signal with a changing waveform and tone character is obtained, and this signal can contain the fundamental frequency and harmonics, or the fundamental frequency can be eliminated leaving only the second harmonic and other higher harmonics.

Referring now to FIG. 6, there is shown a tone generator system embodying this invention. It consists of a master oscillator 19, four flip-flop dividers 20, 21, 22 and 23 of the type shown in FIG. 1, four shaping networks 24, 25, 26 and 27 of the type shown in FIG. 1, four modulators or gates 28, 29, 30 and 31 and four modulating signal sources 32, 33, 34 and v35. The tone generator system also includes resistors R9, R10, R11, R12, R13, R14, R15 and R16 and output terminals 36, 37, 38 and 39.

Each flip-flop divider has output terminals 17 and 18 corresponding to terminals 17 and 18 of the flip-flop divider of FIG. 1. Each flip-flop divider also has a trigger signal input terminal 11 corresponding to the trigger signal input terminal 11 of the flip-flop divider of FIG. 1. Each flip-flop divider except the last one also has an output terminal 18a connected to its output terminal 18.

The output terminal 40 of master oscillator 19 is connected to input terminal 11 of the first flip-flop divider 20, and the flip-flop dividers are connected in cascade as shown.

It can be seen by reference to FIG. 6 that the tone generator system includes four identical units each composed of a flip-flop divider, a shaping network, a modulator, a modulating signal source and two resistors. Consequently, a description of only one such unit is required. Thus, output terminal 17 of flip-flop 20 is connected to the input terminal 41 of modulator 28. 'An amplitude modulating signal is applied from modulating signal source 32 to a modulating signal input terminal 43 of modulator 28. Output terminal 18 of flip-flop 20 is connected to the input terminal 44 of shaping network 24. The output terminal 42 of modulator 28 is connected via resistor R9 to output terminal 36, while the output terminal 15 (see also FIG. 1) of shaping network 24 is connected via resistor R10 to output terminal 36.

A modification of the network just described is shown in FIG. 7. The modification consists of the inclusion of another modulator 45 hetween output terminal 15 of shaping network 24 and resistor R10. The modulating signal input terminal 46 of modulator 45 is supplied with a modulating signal from modulating signal source 32 that is out of phase with the modulating signal supplied to modulating signal input terminal 43 of modulator 28. In such a system both the shaped and the unshaped waveforms are modulated before being added and maximum depth of modulation can be achieved.

In FIG. 9 there is shown one of the units of FIG. 6 in greater detail. Shaping network 24 consists of resistor R7,

capacitor C5 and diode D2, which also are shown'in FIG. 1. Consequently, the signal appearing at output terminal is the same as the signal shown in FIG. 2b but is 180 out of phase therewith, it being understood that flip-flop divider is of the type shown in FIG. 1. The signal appearing at output terminal 17 of flip-flop divider 20 is the same as the signal shown in FIG. 2a but is 180 out of phase therewith. Modulator or gate 28 simply consists of a diode D3 having its cathode connected to output terminal 17 and its anode connected to output terminal 42, which also is the modulating signal input terminal 43 shown in FIG. 6. Modulating signal source 32 is a low frequency (e.g., 1 to 7 Hz.) oscillator of the twin T type with an emitter follower stage comprising a transistor TR3 and an output resistor R17. The modulating signal from modulating signal source 32 is supplied to modulator 28 via a resistor R18 connected between terminal 42 and the emitter electrode of transistor TR3. This modulating signal may be of the type shown in FIG. 8. The frequency of the modulating signal may be varied by means of a potentiometer P1.

The effect of supplying the positive amplitude modulating signal of FIG. 8 to modulator 28 is to vary the signal appearing at output terminal 17 from zero to a maximum. This signal is added via resistors R9 and R10 with the shaped signal appearing at terminal 15 to produce a signal at output terminal 36 that varies in waveform from the waveform of FIG'. 2b to the waveform of FIG. 20. The rate of variation is determined by the frequency of the modulating signal, while intensity is dependent upon the amplitude of the modulating signal. Thus, a composite output signal is produced at terminal 36 that changes character at a predetermined rate and intensity depending upon the frequency and amplitude of the modulating signal. It will be understood that output terminal 36 and output terminals 37, 38 and 39 are connected to key switches which may be connected conventionally via a bus amplifier, voicing circuits and a final amplifier to the loudspeaker of the electronic organ. Of course, rather than modulating the unshaped signal, it would be pos sible to modulate the shaped signal. Also, as shown in FIG. 7, both the shaped and the unshaped signals can be modulated with out of phase modulating signals.

Chorus or celeste effects are created with the tone generator system of FIG. 6 when the various modulating signal sources 32 to thereof produce signals at different frequencies.

Referring now to FIG. 10, there are shown the four modulating signal sources 32, 33, 34 and 35 of FIG. 6 and 48 control terminals that control 48 outputs of 48 flipflop dividers. The control terminals correspond to terminal 42 shown in FIGS. 6 and 9 and are arranged in musical scale sequence from'left to right and octavely related sequence from top to bottom. The modulating signals supplied by modulating signal sources 32 to 35 are shown in FIGS. 11a, 11b, 110 and 11d respectively. As may be seen by reference to these figures, the frequency of the signals decreases from FIG. 11a to FIG. 11d. The modulating signal sources are connected to the control terminals in a way that permits a different modulating signal to be supplied for all octavely related notes as well as notes in the scale that are spaced more than three semitones apart. A chorus effect will be created using the arrangement of FIG. 10 when the four modulating signal sources supply signals at four different frequencies, as shown in FIGS. 11m to 11d, thereby altering the character of the octavely related tones as well as the tones that are spaced more than three semitones apart at different rates.

A more elaborate arrangement is shown in FIG. 12. Each of the lower 16 blocks in FIG. 12 is a modulating signal source, and the numbers in the different blocks indicate the frequencies of the modulating signals supplied by the respective modulating signal sources. 48 control terminals like those shown in FIG. 10 are provided, but

arranged so that only three adjacent semitones receive the same modulating signal. The frequencies of the modulating signals are graduated in steps of about 10%, so that each group of three semitones receives a modulating signal that is slightly higher in frequency as the musical scale is ascended from low to high. The effect is similar to the graduated tuning of a set of celeste pipes in a pipe organ.

The master oscillators 19 for the notes in the musical scale from C to B are shown in FIG. 12. The master oscillators are connected in groups of three to the modulating signal sources producing signals with the following frequencies: 6.26, 6.88, 7.56 and 8.32. These signals frequency modulate the master oscillators at varying rates. The result of this is that a chorus effect is achieved even when only a single note is played, while an enhanced chorus effect is achieved when a number of notes are played together. It will be understood, of course, that the signals from the four modulating signal sources designated above are injected into the master oscillators at points where they will cause frequency modulation of the output signals of the master oscillators. Of course, more or fewer than four of the modulating signal sources can be employed for frequency modulating the output signals of the master oscillators.

It should be noted that in order to obtain a chorus or celeste effect, it is essential for the frequencies of the modulating signals supplied by the modulating signal sources to be different from each other. However, it should be noted that if these frequencies are not different, a tremulant effect will be created. Consequently, the unit shown in FIG. 9, for example, is useful, per se, in creating a tremulant effect, and it also is useful, when used in conjunction with other units having modulating signals of different frequencies, in creating a chorus or celeste effect.

Referring again to FIG. 7, rather than supplying modulator 45 with a modulating signal that is 180 out of phase with the modulating signal supplied to modulator 28, it would be possible to supply the two modulators with two entirely different modulating signals, and an even more complex result would be obtained.

If desirable, a control network can be employed with the modulating signal source 32 of FIG. 9, for example, to ermit the degree of modulation to be varied. In this respect, modulation such as will be achieved using the modulating signal of FIG. 8 is not essential to the invention.

It also would be possible to provide for a player operated control that would shift the frequencies of the modulating signals produced by all modulators by the same percentage, and this control might have, for example, low, medium and high positions.

In order to create a chorus or celeste effect, it is necessary that complete cancellation not result at all times at the various output terminals 36, 37, 38 and 39. It is preferred that complete cancellation should never result, although a degree of cancellation can be tolerated.

It also should be noted that instead of employing frequency dividers, frequency multipliers could be used, and the term frequency modifying device is intended to mean either a divider or a multiplier that produces out of phase signals at its output terminals.

It will be appreciated from the foregoing that many different techniques may be employed either to avoid cancellation completely or, less preferably, to permit only partial cancellation.

While preferred embodiments of this invention have been disclosed herein, those skilled in the art will appreciate that changes and modifications may be made without departing from the spirit and scope of this invention as defined in the appended claims.

What I claim as my invention is:

1. In combination; a tone signal generator having an output terminal and adapted to provide a tone signal at said output terminal; a frequency modifying device having an input terminal and first and second output terminals; means connecting said output terminal of said tone signal generator and said input terminal for supplying said tone signal to said frequency modifying device to be modified thereby, whereby said frequency modifying device provides first and second signals at said first and second output terminals thereof, said first and second signals both having a frequency differing from the frequency of said tone signal; a signal processing network connected to at least one of said first and second output terminals for processing at least one of said first and second signals and including a shaping network for shaping the waveform of one of said signals derived from said frequency modifying device into a waveform different from the waveform of the other of said signals derived from said frequency modifying device and means for amplitude modulating at least one of said signals derived from said frequency modifying device; and means for adding the signals derived from said frequency modifying device after translation by said signal processing network.

2. The invention according to claim 1 wherein there are a plurality of said tone signal generators each adapted to provide a tone of a different frequency, at least one of said frequency modifying devices for each of said tone signal generators and one of said signal processing networks for each of said frequency modifying devices.

3. The invention according to claim 1 wherein said frequency modifying device is a divider, said divider being a bistable flip-flop, whereby said first and second signals at said first and second output terminals respectively are of the same waveform and amplitude but 180" out of phase with each other.

4. The invention according to claim 3 wherein said amplitude modulating means includes an amplitude modulating signal source, and means for varying the frequency o fthe amplitude modulating signal produced by said amplitude modulating signal source.

5. The invention according to claim 2 wherein said amplitude modulating means includes an amplitude modulatingsignal source, at least one of said amplitude modulating signal sources being common to a plurality of said signal processing networks.

6. In combination: a tone signal generator having an output terminal and adapted to provide a tone signal at said output terminal; a plurality of cascade connected frequency modifying devices each having an input terminal and first and second output terminals; means connecting said output terminal of said tone signal generator and said input terminal of the first one of said cascade connected frequency modifying devices for supplying said tone signal to said frequency modifying devices to be modified thereby, whereby said frequency modifying devices each provide first and second signals at said first and second output terminals thereof, said first and second signals produced by each of said frequency modifying devices both having a frequency different from the frequency of said tone signal; a plurality of signal processing networks corresponding in number to the number of frequency modifying devices and connected to at least one of said first and second output terminals of their respective frequency modifying devices for processing at least one of said first and second signals thereof, each said signal processing network including a shaping network for shaping the waveform of one of said signals derived from its respective frequency modifying device into a waveform different from the waveform of the other of said signals derived from its respective frequency modifying device and means for amplitude modulating at least one of said signals derived from its respective frequency modifying device; and a plurality of adding means for adding the signals derived from the respective frequency rn'odifying devices after translation by the respective signal processing networks.

7. The invention according to claim 6 wherein there are a plurality of said tone signal generators each adapted to provide a tone of a different frequency and a set of said cascade connected frequency modifying devices for each of said tone signal generators.

8. The invention according to claim 6 wherein each of said amplitude modulating means includes an amplitude modulating signal source, the frequencies of the amplitude modulating signals produced by said amplitude modulating signal sources being different from each other.

9. The invention according to claim 8 wherein the frequencies of said amplitude modulating signals are substantially lower than the frequencies of said first and second signals.

10. The invention according to claim 7 wherein said frequency modifying devices are frequency dividers.

11. The invention according to claim 10 wherein said dividers are bi-stable flip-flops, whereby each set of said first and second signals at said first and second output terminals resp ctively are of the same waveform and amplitude but out of phase with each other.

12. The invention according to claim 11 wherein each of said amplitude modulating means includes an amplitude modulating signal source, the frequencies of the amplitude modulating signals produced by at least some of said amplitude modulating signal sources being different from each other.

13. The invention according to claim 12 wherein the frequencies of said amplitude modulating signals are substantially lower than the frequencies of said first and second signals.

14. The invention according to claim 8 including means connecting said tone signal generator and one of said amplitude modulating signal sources for frequency modulating said tone signal by the signal produced by said amplitude modulating signal source.

References Cited UNITED STATES PATENTS 2,905,040 9/ 1959 Hanert. 3,000,252 9/1961 Wayne 84----1.11 X 3,004,460 1'0/ 1961 Wayne 841.11 X 3,007,361 11/ 1961 Wayne.

3,093,700 '6/1963 George 841.22 3,355,539 1l/1967 Munch et a1. 841.23

HERMAN K. SAALBACH, Primary Examiner T. P. VEZEAU, Assistant Examiner US. or. X.R. 84-1.22, 12 4 

